Showing papers on "Thermoelastic damping published in 1982"
TL;DR: In this paper, the authors developed a one-dimensional model for thermal wave depth profiling that provides expressions for the temperature at the surface of the sample and for the thermoelastic response beneath the surface.
Abstract: We have developed a one‐dimensional model for thermal‐wave depth profiling that provides expressions for the temperature at the surface of the sample and for the thermoelastic response beneath the surface. The model shows that elastic wave interference effects produce significant differences between samples with mechanically free and constrained surfaces, and that thermal‐ wave images of thermal conductivity variations are obtainable from the thermoelastic signal only if the front surface is mechanically free. We have also considered the case of subsurface heating and found that for heating occurring at depths of more than a few thermal diffusion lengths, the thermoelastic signal becomes independent of thermal conductivity variations. This has important implications for thermal‐wave image range and resolution.
236 citations
TL;DR: In this article, a line-focusing Q-switched Nd: YAG laser pulses are projected onto metal surfaces with a cylindrical lens, and the resulting ultrasonic frequency components of the resultant Rayleigh waves are shown to be emitted preferentially broadside from the line-source in narrow beams.
104 citations
TL;DR: The transmission of impact forces in a straight leg from the foot to the level of the greater trochanter was investigated by a two-degree of freedom linear damped-spring model and satisfactory prediction of the magnitudes of the first two peaks of the acceleration was achieved in the two subjects studied.
Abstract: The transmission of impact forces in a straight leg from the foot to the level of the greater trochanter was investigated by a two-degree of freedom linear damped-spring model. Foot ground forces measured during a vertical jump and accelerations measured at the level of the greater trochanter were used as model input. The model elastic constant and damping coefficient were determined by solving the dynamic equations of the system. The model was used to predict peak acceleration values for a given input force. Satisfactory prediction of the magnitudes of the first two peaks of the acceleration (maximum difference of 3 percent) was achieved in the two subjects studied.
79 citations
TL;DR: In this article, Green's functions are given which permit the solution of the former problem to be expressed as a double integral of the surface heat input or temperature in time and space.
65 citations
TL;DR: In this article, a new technique for recording stress patterns called thermoelastic stress analysis (TSA) is described, which measures the distribution of stress on the surface of a structure under load, and the connection between stress concentration, mechanical design and safety.
Abstract: After discussions on the need to measure the distribution of stress on the surface of a structure under load, and the connection between stress concentration, mechanical design and safety, a new technique for recording stress patterns called thermoelastic stress analysis (TSA) is described. For given material constants, the change in temperature on the surface of a structure, subject to dynamic loading, is directly proportional to the change in stress at that point. A specially designed, high-sensitivity I.R. camera is described which can present a colour display of the distribution of stress which could arise from temperature variations as small as 0·001 K resulting from a few units of microstrain in metals. A selection of typical results obtained by recording the stress concentration on the surface of a model pedestal structure are given to illustrate how TSA could be used as an aid to design. The likely useful areas of application of TSA can be identified with the help of a list of the principal charac...
60 citations
TL;DR: In this article, the acoustic emission activity accompanying thermoelastic martensitic phase change in Au-47.5 at.% Cd alloy during the forward and reverse transformations was found to be asymmetric in energy and pulsewidth distribution.
42 citations
TL;DR: In this paper, the one-dimensional axisymmetric quasi-static coupled thermoelastic problem is investigated and the general solutions of its governing equations are obtained in the transform domain.
Abstract: The one-dimensional axisymmetric quasi-static coupled thermoelastic problem is investigated. The general solutions of its governing equations are obtained in the transform domain. The solutions in the real domain for the cases of an infinitely long solid cylinder and for an infinite medium with a cylindrical hole are also presented. The solution technique uses Laplace transform, and the inversion to the real domain is obtained by means of Cauchy's theorem of residues and the convolution theorem. Comparison with published results, when similar assumptions are made and the same boundary conditions are imposed, shows complete agreement.
33 citations
TL;DR: In this paper, the properties of high damping alloys, such as Mn-Cu alloy and Fe-Cr-Al alloy, were studied with a view to assessing the damping characteristics.
Abstract: The viscoelastic behaviors of two kinds of high damping alloys, Mn-Cu alloy and Fe-Cr-Al alloy, are studied with a view to assessing the damping characteristics. Under the assumption that the material is a linear viscoelastic body, the complex compliance is obtained from the wave propagation data on a long rod analyzed with Fourier transform technique. Copper is also examined for comparison. Experimental results reveal the frequency and amplitude dependences of damping capacity in each material. It is also found that the 4-element model should be applied for both high damping alloys, and the Maxwell model for copper, respctively.
32 citations
TL;DR: In this article, a method for the calculation of temperature in the shoe-film-rotor assembly of a thrust bearing is presented, which allows reverse flow to occur and simplifies the calculations of hot oil carry-over.
26 citations
TL;DR: In this article, a solution for the frictionless thermoelastic contact of a cooled flat cylindrical rigid punch and an elastic half-space is given, where a central circle is in imperfect contact, i.e., a non-zero contact resistance exists between the surfaces.
Abstract: SUMMARY A solution is given for the frictionless thermoelastic contact of a cooled flat cylindrical rigid punch and an elastic half-space. If the thermal distortion is sufficiently small, contact is retained over the entire punch face and the solution can be written down from known results. For larger temperature differences the conventional boundary conditions do not permit a solution, but a solution is here developed in which a central circle is in imperfect contact, i.e. a non-zero contact resistance exists between the surfaces. The problem is reduced to a boundary-value problem in potential theory using a solution of the thermoelastic equations in two harmonic functions. These functions are written as the sum of a number of components each of which satisfies two-part boundary conditions. The resulting boundary conditions lead to coupled Abel integral equations which are reduced to a single Fredholm equation by substitution. Results are given for typical contact pressure distributions and for the relationship between load, temperature difference, heat flux and the radius of the imperfect contact region.
23 citations
TL;DR: In this paper, first and second derivatives of cohesion energy of forsterite with respect to cell edges (generalized Born-Mayer model) are related to thermoelastic tensors; first derivatives with respect of five structural parameters (rotation angle of the SiO4 tetrahedron, translations of Si and Mg(2) atoms) are set equal to zero by the zero-force principle.
TL;DR: In this article, the authors presented analytic solutions and numerical results of the scattering of plane sound waves from a thermoelastic circular cylinder and from a thermodynamic sphere in an infinite, thermoviscous fluid medium.
Abstract: This paper presents analytic solutions and numerical results of the scattering of plane sound waves from a thermoelastic circular cylinder and from a thermoelastic sphere in an infinite, thermoviscous fluid medium. The thermoelastic properties of the cylinder and the sphere and the viscosity and thermal conductivity of the surrounding fluid are taken into consideration in the solutions of the acoustic‐scattering problems. We started with examining the acoustic field equations in thermoviscous fluids and in thermoelastic solids from the standpoints of continuum mechanics and thermodynamics, and then presented the normal‐mode solutions to, and numerical examples of, the acoustic scattering by a single cylinder and a sphere. The acoustic parameters of interest are the farfield scattering pattern, the acoustic‐radiation force, and the absorption and scattering cross sections. These parameters were first derived in closed forms and then evaluated numerically for a given set of material properties.
TL;DR: In this paper, the mobility of s-γ[MATH] martensitic interfaces in thermoelastic s-CuAlNi alloys is investigated using stress-assisted single interface transformations over a temperature range of 180 to 410K and imposed interfacial velocities of 10-6 to 10-2 m/s.
Abstract: The mobility of s-γ[MATH] martensitic interfaces in thermoelastic s-CuAlNi alloys is investigated using stress-assisted single interface transformations over a temperature range of 180 to 410K and imposed interfacial velocities of 10-6 to 10-2 m/s. The behavior is consistent with thermally-activated interfacial motion, although an anomalous temperature dependence is observed below 210K which may be due to elastic softening. Measured activation energies of 0.3 to 0.4 eV (4.5 x 10-20 to 6.5 x 10-20 J) and activation volumes of 103 to 104 atomic volumes suggest that motion of the interface above 210K is controlled by interaction with discrete particles or clusters.
TL;DR: In this paper, it has been shown that simple deformation of solids is accompanied by inversion of internal energy which is controlled by coefficient of thermal expansion, and that the volume (irrotational) elasticity of amorphous regions rather than by shape elasticity typical of rubber elasticity.
Abstract: Thermodynamic aspects of reversible simple extension of solid polymers have been considered in terms of the conventional equation of state and equations have been obtained for the thermodynamic functions. It is shown that simple deformation of solids is accompanied by inversion of internal energy which is controlled by coefficient of thermal expansion. Work, heat and internal energy as functions of strain have been determined by deformation calorimetry for the typical glass-like and crystalline polymers and it has been found that in uniaxially oriented crystalline polymers at aboveT
g
the internal energy undergoes inversion due to the negative coefficient of thermal expansion. It has been demonstrated that the thermoelastic behaviour of two-phase crystalline polymers is controlled by the volume (irrotational) elasticity of amorphous regions rather than by shape elasticity typical of rubber elasticity. From this position, a thermophysical analysis of the deformation of the basic models of oriented crystalline polymers and combined investigation of the thermal phenomena and structural changes in oriented PE and PP have been carried out. It has been shown that the Peterlin-Prevorsek model which implies existence of both intra- and interfibrillar amorphous regions quite adequately account for the thermophysical and structural effect observed in tension of the oriented specimens in the original and annealed state. Thermoelastic properties of super-oriented crystalline polymers have also been discussed in brief.
TL;DR: In this article, the authors determined the thermoelastic stresses within an arbitrary inclusion and in its neighborhood by using one of the modifications of the self-consistent field method /1/ that permits taking account of interaction of the inclusions.
TL;DR: In this article, a three-dimensional theoretical treatment for the thermal-stress problems in spherical coordinates is developed, where the first part is devoted to the relations of stress components in terms of thermoelastic displacement potential and a harmonic function.
Abstract: A three-dimensional theoretical treatment for the thermal-stress problems in spherical coordinates is developed. The first part is devoted to the relations of stress components in terms of thermoelastic displacement potential and a harmonic function. Next, a hollow sphere with a rotating heat source is considered as an illustrative example. The numerical calculations are then also carried out and the results shown graphically.
TL;DR: In this article, a method based on ever occurring thermal emission in samples under stress is presented to identify the true macroscopic flow stress or point of physical yielding in 38NCD4 steel.
TL;DR: In this article, invariant integrals are derived for coupled time dependent thermoviscoelastic solids with spatially varying moduli, which are used to obtain crack tip stress and displacement fields for certain special strip problems where constant temperatures and displacements are applied to the strip sides.
TL;DR: An abrupt decrease in acoustic loss was observed in flexural modes of polycrystalline Nb disk samples on cooling through the superconducting transition temperature T/sub c/ as discussed by the authors.
Abstract: An abrupt decrease in acoustic loss Q/sup -1/ has been observed in flexural modes of polycrystalline Nb disk samples on cooling through the superconducting transition temperature T/sub c/ High-resolution measurements on a 16-kHz mode of one sample showed a 30% decrease in Q/sup -1/ in a 20-mK temperature interval It is shown that these results are clearly identifiable with the reduction of the thermoelastic contribution to the acoustic loss in the superconducting state
TL;DR: In this article, single crystals of optical quality of isotypic Li2SiO3, Li2GeO3 and Na2GO3 have been grown from the melt using the Czochralski technique.
Abstract: Single crystals of optical quality of isotypic Li2SiO3, Li2GeO3, and Na2GeO3, space group Ccm21, with diameters of ca 16 mm and lengths of ca 20 mm (Li2SiO3) and ca 60 mm (Li2GeO3 and Na2GeO3) have been grown from the melt using the Czochralski technique. On Li2SiO3, Li2GeO3, and Na2GeO3 pyroelectric coefficients and complete dielectric, piezoelectric, elastic, and thermoelastic tensor properties have been determined; the latter from the temperature dependence of resonance frequencies. All crystals investigated exhibited only a small amount of 180° twins. They all possess large pyroelectric coefficients about-five times that of tourmaline. The longitudinal piezoelectric constant d333 is about five times larger than d111 of alpha quartz. Qualitative measurements on Na2SiO3 revealed similar values of pyroelectric and piezoelectric effects. The technical application of these crystals encounters some difficulties: Li2SiO3 is excellently cleavable parallel (010). This face contains the polar direction [001]. Na2GeO3 suffers from chemical decomposition in humid atmosphere and is well cleavable too. Both happens to a much less extent in Li2GeO3. Na2SiO3 proved to be hardly suitable for any application of its polar properties due to its bad chemical stability against humid air and its excellent cleavage.
TL;DR: In this article, the main objective of this contribution is to offer evidence of the need to revisit the field of the mechanical behavior of metals, taking advantage of basic physical concepts which have almost systematically been neglected in materials research.
Abstract: The main objective of this contribution is to offer evidence of the need to revisit the field of the mechanical behavior of metals, taking advantage of basic physical concepts which have almost systematically been neglected in materials research.
TL;DR: In this paper, a finite element code CHICAMC was used to calculate the residual stress fields in whole and hollow pellets in a radial temperature field of approximately parabolic shape.
TL;DR: In this article, a generalization of Kirchhoff's theorem for the classical wave equation to the case of a central system of field equations of coupled thermoelasticity is established.
Abstract: A generalization of Kirchhoff's theorem for the classical wave equation to the case of a central system of field equations of coupled thermoelasticity is established in this paper. The theorem asserts that a pair (Φ, θ), where Φ and θ denote the thermoelastic displacement potential and temperature, respectively, can be expressed by surface integrals over the boundary of a thermoelastic solid whose kernels have the form of an infinite series satisfying the wave-like and heat-like equations occurring in the decomposition theorem for the central system of equations ([3]).
TL;DR: In this paper, an attempt is made to study the propagation of weak shock waves in heat conducting materials, and the equation for determining the velocities of propagation is derived and expressions for the velocity in linear elastic materials are obtained.
TL;DR: In this paper, an analysis of the thermoelastic action of high-power pulse-periodic laser radiation on the surface of a solid is made using relationships, similar to Duhamel integrals, between the characteristics of the thermally stressed state on exposure to cw and arbitrarily time-varying laser radiation.
Abstract: An analysis is made of the thermoelastic action of high-power pulse-periodic laser radiation on the surface of a solid. The analysis is made using relationships, similar to Duhamel integrals, between the characteristics of the thermally stressed state on exposure to cw and arbitrarily time-varying laser radiation. Calculations are made of the dependences of the maximum laser radiation intensities causing impermissible elastic distortions of the surface, plastic flow of the material resulting in residual stresses, fatigue failure and melting of the surface layer.
01 Jan 1982
TL;DR: The source of residual stresses in ceramics cannot be different in the absence of externally applied loads and body forces, and they arise either from non-uniform irreversible stress relaxation or from nonuniformities in thermo-elastic or compositionelastic properties within the specimen as mentioned in this paper.
Abstract: The source of residual stresses, i. e., those stresses that persist in the absence of externally applied loads and body forces, cannot be different in ceramics than they are in other classes of material. They arise either from non-uniform irreversible stress relaxation or from non-uniformities in thermoelastic or compositionelastic* properties within the specimen. Not surprisingly, residual stresses in ceramics can be extremely beneficial, detrimental, or somewhere in between.
01 Jan 1982
TL;DR: The photoacoustic effect as mentioned in this paper is a phenomenon in which a substantial fraction of the annihilated photon's energy is transformed into heat, and the heat pulses are exponentially damped as they move away from the source with relatively little attenuation.
Abstract: In many light-absorbing materials a substantial fraction of the annihilated photon’s energy is transformed into heat. If the light is pulsed, then pulses of heat are produced which, in turn, generate pulsed elastic disturbances; this phenomenon is commonly known as the photoacoustic effect. Whereas the heat pulses are exponentially damped as they move away from the source, the elastic waves propagate with relatively little attenuation. The elastic waves so generated contain information about the thermal, elastic, and optical properties of the material in which they are produced as well as information about materials in contact with the generating material. The information carried by the elastic wave is more localized--that is, the resolution is greater-- the higher is the frequency of the light pulses; and if the frequency is increased to the microwave range, the resolution can approach or even surpass that of the optical microscope. The generation of high-frequency elastic waves by photothermal means is of current interest because of its relevance to several areas of physics, including: the development of the photoacoustic microscope1 , thermal-wave imaging2 , determination of thermoelastic material parameters, nondestructive evaluation of devices3 , and laser annealing and melting phenomena in semiconductors.